src/shared/pager.c

   1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
   2
   3 #include <errno.h>
   4 #include <stddef.h>
   5 #include <stdint.h>
   6 #include <stdio.h>
   7 #include <stdlib.h>
   8 #include <sys/prctl.h>
   9 #include <unistd.h>
  10
  11 #include "sd-login.h"
  12
  13 #include "copy.h"
  14 #include "env-util.h"
  15 #include "fd-util.h"
  16 #include "fileio.h"
  17 #include "io-util.h"
  18 #include "locale-util.h"
  19 #include "log.h"
  20 #include "macro.h"
  21 #include "pager.h"
  22 #include "process-util.h"
  23 #include "rlimit-util.h"
  24 #include "signal-util.h"
  25 #include "string-util.h"
  26 #include "strv.h"
  27 #include "terminal-util.h"
  28
  29 static pid_t pager_pid = 0;
  30
  31 static int stored_stdout = -1;
  32 static int stored_stderr = -1;
  33 static bool stdout_redirected = false;
  34 static bool stderr_redirected = false;
  35
  36 _noreturn_ static void pager_fallback(void) {
  37         int r;
  38
  39         r = copy_bytes(STDIN_FILENO, STDOUT_FILENO, UINT64_MAX, 0);
  40         if (r < 0) {
  41                 log_error_errno(r, "Internal pager failed: %m");
  42                 _exit(EXIT_FAILURE);
  43         }
  44
  45         _exit(EXIT_SUCCESS);
  46 }
  47
  48 static int no_quit_on_interrupt(int exe_name_fd, const char *less_opts) {
  49         _cleanup_fclose_ FILE *file = NULL;
  50         _cleanup_free_ char *line = NULL;
  51         int r;
  52
  53         assert(exe_name_fd >= 0);
  54         assert(less_opts);
  55
  56         /* This takes ownership of exe_name_fd */
  57         file = fdopen(exe_name_fd, "r");
  58         if (!file) {
  59                 safe_close(exe_name_fd);
  60                 return log_error_errno(errno, "Failed to create FILE object: %m");
  61         }
  62
  63         /* Find the last line */
  64         for (;;) {
  65                 _cleanup_free_ char *t = NULL;
  66
  67                 r = read_line(file, LONG_LINE_MAX, &t);
  68                 if (r < 0)
  69                         return log_error_errno(r, "Failed to read from socket: %m");
  70                 if (r == 0)
  71                         break;
  72
  73                 free_and_replace(line, t);
  74         }
  75
  76         /* We only treat "less" specially.
  77          * Return true whenever option K is *not* set. */
  78         r = streq_ptr(line, "less") && !strchr(less_opts, 'K');
  79
  80         log_debug("Pager executable is \"%s\", options \"%s\", quit_on_interrupt: %s",
  81                   strnull(line), less_opts, yes_no(!r));
  82         return r;
  83 }
  84
  85 void pager_open(PagerFlags flags) {
  86         _cleanup_close_pair_ int fd[2] = EBADF_PAIR, exe_name_pipe[2] = EBADF_PAIR;
  87         _cleanup_strv_free_ char **pager_args = NULL;
  88         _cleanup_free_ char *l = NULL;
  89         const char *pager, *less_opts;
  90         int r;
  91
  92         if (flags & PAGER_DISABLE)
  93                 return;
  94
  95         if (pager_pid > 0)
  96                 return;
  97
  98         if (terminal_is_dumb())
  99                 return;
 100
 101         if (!is_main_thread())
 102                 return (void) log_error_errno(SYNTHETIC_ERRNO(EPERM), "Pager invoked from wrong thread.");
 103
 104         pager = getenv("SYSTEMD_PAGER");
 105         if (!pager)
 106                 pager = getenv("PAGER");
 107
 108         if (pager) {
 109                 pager_args = strv_split(pager, WHITESPACE);
 110                 if (!pager_args)
 111                         return (void) log_oom();
 112
 113                 /* If the pager is explicitly turned off, honour it */
 114                 if (strv_isempty(pager_args) || strv_equal(pager_args, STRV_MAKE("cat")))
 115                         return;
 116         }
 117
 118         /* Determine and cache number of columns/lines before we spawn the pager so that we get the value from the
 119          * actual tty */
 120         (void) columns();
 121         (void) lines();
 122
 123         if (pipe2(fd, O_CLOEXEC) < 0)
 124                 return (void) log_error_errno(errno, "Failed to create pager pipe: %m");
 125
 126         /* This is a pipe to feed the name of the executed pager binary into the parent */
 127         if (pipe2(exe_name_pipe, O_CLOEXEC) < 0)
 128                 return (void) log_error_errno(errno, "Failed to create exe_name pipe: %m");
 129
 130         /* Initialize a good set of less options */
 131         less_opts = getenv("SYSTEMD_LESS");
 132         if (!less_opts)
 133                 less_opts = "FRSXMK";
 134         if (flags & PAGER_JUMP_TO_END) {
 135                 l = strjoin(less_opts, " +G");
 136                 if (!l)
 137                         return (void) log_oom();
 138                 less_opts = l;
 139         }
 140
 141         /* We set SIGINT as PR_DEATHSIG signal here, to match the "K" parameter we set in $LESS, which enables SIGINT behaviour. */
 142         r = safe_fork("(pager)", FORK_RESET_SIGNALS|FORK_DEATHSIG_SIGINT|FORK_RLIMIT_NOFILE_SAFE|FORK_LOG, &pager_pid);
 143         if (r < 0)
 144                 return;
 145         if (r == 0) {
 146                 const char *less_charset;
 147
 148                 /* In the child start the pager */
 149
 150                 if (dup2(fd[0], STDIN_FILENO) < 0) {
 151                         log_error_errno(errno, "Failed to duplicate file descriptor to STDIN: %m");
 152                         _exit(EXIT_FAILURE);
 153                 }
 154
 155                 safe_close_pair(fd);
 156
 157                 if (setenv("LESS", less_opts, 1) < 0) {
 158                         log_error_errno(errno, "Failed to set environment variable LESS: %m");
 159                         _exit(EXIT_FAILURE);
 160                 }
 161
 162                 /* Initialize a good charset for less. This is particularly important if we output UTF-8
 163                  * characters. */
 164                 less_charset = getenv("SYSTEMD_LESSCHARSET");
 165                 if (!less_charset && is_locale_utf8())
 166                         less_charset = "utf-8";
 167                 if (less_charset &&
 168                     setenv("LESSCHARSET", less_charset, 1) < 0) {
 169                         log_error_errno(errno, "Failed to set environment variable LESSCHARSET: %m");
 170                         _exit(EXIT_FAILURE);
 171                 }
 172
 173                 /* People might invoke us from sudo, don't needlessly allow less to be a way to shell out
 174                  * privileged stuff. If the user set $SYSTEMD_PAGERSECURE, trust their configuration of the
 175                  * pager. If they didn't, use secure mode when under euid is changed. If $SYSTEMD_PAGERSECURE
 176                  * wasn't explicitly set, and we autodetect the need for secure mode, only use the pager we
 177                  * know to be good. */
 178                 int use_secure_mode = secure_getenv_bool("SYSTEMD_PAGERSECURE");
 179                 bool trust_pager = use_secure_mode >= 0;
 180                 if (use_secure_mode == -ENXIO) {
 181                         uid_t uid;
 182
 183                         r = sd_pid_get_owner_uid(0, &uid);
 184                         if (r < 0)
 185                                 log_debug_errno(r, "sd_pid_get_owner_uid() failed, enabling pager secure mode: %m");
 186
 187                         use_secure_mode = r < 0 || uid != geteuid();
 188
 189                 } else if (use_secure_mode < 0) {
 190                         log_warning_errno(use_secure_mode, "Unable to parse $SYSTEMD_PAGERSECURE, assuming true: %m");
 191                         use_secure_mode = true;
 192                 }
 193
 194                 /* We generally always set variables used by less, even if we end up using a different pager.
 195                  * They shouldn't hurt in any case, and ideally other pagers would look at them too. */
 196                 r = set_unset_env("LESSSECURE", use_secure_mode ? "1" : NULL, true);
 197                 if (r < 0) {
 198                         log_error_errno(r, "Failed to adjust environment variable LESSSECURE: %m");
 199                         _exit(EXIT_FAILURE);
 200                 }
 201
 202                 if (trust_pager && pager_args) { /* The pager config might be set globally, and we cannot
 203                                                   * know if the user adjusted it to be appropriate for the
 204                                                   * secure mode. Thus, start the pager specified through
 205                                                   * envvars only when $SYSTEMD_PAGERSECURE was explicitly set
 206                                                   * as well. */
 207                         r = loop_write(exe_name_pipe[1], pager_args[0], strlen(pager_args[0]) + 1);
 208                         if (r < 0) {
 209                                 log_error_errno(r, "Failed to write pager name to socket: %m");
 210                                 _exit(EXIT_FAILURE);
 211                         }
 212
 213                         execvp(pager_args[0], pager_args);
 214                         log_full_errno(errno == ENOENT ? LOG_DEBUG : LOG_WARNING, errno,
 215                                        "Failed to execute '%s', using fallback pagers: %m", pager_args[0]);
 216                 }
 217
 218                 /* Debian's alternatives command for pagers is called 'pager'. Note that we do not call
 219                  * sensible-pagers here, since that is just a shell script that implements a logic that is
 220                  * similar to this one anyway, but is Debian-specific. */
 221                 static const char* pagers[] = { "pager", "less", "more", "(built-in)" };
 222
 223                 for (unsigned i = 0; i < ELEMENTSOF(pagers); i++) {
 224                         /* Only less (and our trivial fallback) implement secure mode right now. */
 225                         if (use_secure_mode && !STR_IN_SET(pagers[i], "less", "(built-in)"))
 226                                 continue;
 227
 228                         r = loop_write(exe_name_pipe[1], pagers[i], strlen(pagers[i]) + 1);
 229                         if (r < 0) {
 230                                 log_error_errno(r, "Failed to write pager name to socket: %m");
 231                                 _exit(EXIT_FAILURE);
 232                         }
 233
 234                         if (i < ELEMENTSOF(pagers) - 1) {
 235                                 execlp(pagers[i], pagers[i], NULL);
 236                                 log_full_errno(errno == ENOENT ? LOG_DEBUG : LOG_WARNING, errno,
 237                                                "Failed to execute '%s', will try '%s' next: %m", pagers[i], pagers[i+1]);
 238                         } else {
 239                                 /* Close pipe to signal the parent to start sending data */
 240                                 safe_close_pair(exe_name_pipe);
 241                                 pager_fallback();
 242                                 assert_not_reached();
 243                         }
 244                 }
 245         }
 246
 247         /* Return in the parent */
 248         stored_stdout = fcntl(STDOUT_FILENO, F_DUPFD_CLOEXEC, 3);
 249         if (dup2(fd[1], STDOUT_FILENO) < 0) {
 250                 stored_stdout = safe_close(stored_stdout);
 251                 return (void) log_error_errno(errno, "Failed to duplicate pager pipe: %m");
 252         }
 253         stdout_redirected = true;
 254
 255         stored_stderr = fcntl(STDERR_FILENO, F_DUPFD_CLOEXEC, 3);
 256         if (dup2(fd[1], STDERR_FILENO) < 0) {
 257                 stored_stderr = safe_close(stored_stderr);
 258                 return (void) log_error_errno(errno, "Failed to duplicate pager pipe: %m");
 259         }
 260         stderr_redirected = true;
 261
 262         exe_name_pipe[1] = safe_close(exe_name_pipe[1]);
 263
 264         r = no_quit_on_interrupt(TAKE_FD(exe_name_pipe[0]), less_opts);
 265         if (r > 0)
 266                 (void) ignore_signals(SIGINT);
 267 }
 268
 269 void pager_close(void) {
 270
 271         if (pager_pid <= 0)
 272                 return;
 273
 274         /* Inform pager that we are done */
 275         (void) fflush(stdout);
 276         if (stdout_redirected)
 277                 if (stored_stdout < 0 || dup2(stored_stdout, STDOUT_FILENO) < 0)
 278                         (void) close(STDOUT_FILENO);
 279         stored_stdout = safe_close(stored_stdout);
 280         (void) fflush(stderr);
 281         if (stderr_redirected)
 282                 if (stored_stderr < 0 || dup2(stored_stderr, STDERR_FILENO) < 0)
 283                         (void) close(STDERR_FILENO);
 284         stored_stderr = safe_close(stored_stderr);
 285         stdout_redirected = stderr_redirected = false;
 286
 287         (void) kill(pager_pid, SIGCONT);
 288         (void) wait_for_terminate(TAKE_PID(pager_pid), NULL);
 289         pager_pid = 0;
 290 }
 291
 292 bool pager_have(void) {
 293         return pager_pid > 0;
 294 }
 295
 296 int show_man_page(const char *desc, bool null_stdio) {
 297         const char *args[4] = { "man", NULL, NULL, NULL };
 298         char *e = NULL;
 299         pid_t pid;
 300         size_t k;
 301         int r;
 302
 303         k = strlen(desc);
 304
 305         if (desc[k-1] == ')')
 306                 e = strrchr(desc, '(');
 307
 308         if (e) {
 309                 char *page = NULL, *section = NULL;
 310
 311                 page = strndupa_safe(desc, e - desc);
 312                 section = strndupa_safe(e + 1, desc + k - e - 2);
 313
 314                 args[1] = section;
 315                 args[2] = page;
 316         } else
 317                 args[1] = desc;
 318
 319         r = safe_fork("(man)", FORK_RESET_SIGNALS|FORK_DEATHSIG_SIGTERM|(null_stdio ? FORK_REARRANGE_STDIO : 0)|FORK_RLIMIT_NOFILE_SAFE|FORK_LOG, &pid);
 320         if (r < 0)
 321                 return r;
 322         if (r == 0) {
 323                 /* Child */
 324                 execvp(args[0], (char**) args);
 325                 log_error_errno(errno, "Failed to execute man: %m");
 326                 _exit(EXIT_FAILURE);
 327         }
 328
 329         return wait_for_terminate_and_check(NULL, pid, 0);
 330 }